This paper describes the study on overlay accuracy of reticles, using a reticle set for DRAM. It is found that single reticle pattern placement has to be higher accuracy than overlay of reticles, which may be a majority in the total overlay accuracy. Concerning some points of a reticle set, we found that there is a very large value. To match overlay accuracy of reticles with the demand of devices, we have shown that the suitable reticle exposure system has to be used and managed exactly. In order to assure overlay accuracy of a reticle set, it was proposed that single reticle pattern placement accuracy must be higher than overlay accuracy demand and the overlay accuracy yield also should be shown in some cases.